Underframes refer to the lower framework or structure of a vehicle or machinery on which the body or other components are mounted. Synonyms for underframes include chassis, frame, subframe, substructure, base, foundation, bed, platform, groundwork, infrastructure, and skeleton. The term chassis is often used in the automobile industry to refer to the underframe or basic structure of a vehicle. Similarly, the term subframe is commonly used in construction to refer to a smaller supporting frame that is attached to the main frame of a building. The underframe or foundation of any structure or vehicle is critical to its strength and stability, and therefore, the terms used to describe it must be selected with care.